The present disclosure relates to measurement of current in aerospace applications and, more particularly, to the use of an unshielded Hall Effect sensor to measure the current supplied to a heater on an aircraft or air vehicle (such as a missile or other self-propelled munition).
In aerospace equipment, such as air data probes (e.g., pitot tubes) or total air temperature sensors, there is a need to use heaters to melt ice or prevent ice from forming on these atmospheric probes. Often, the current used to power the heater (called the heater current) is isolated from the current used to power the electronics that adjust/control the dissipation of heat from the heater. Therefore, a system is needed to measure the current supplied to the heater and communicate that measurement to the electronics that adjust/control the heater current.
One system utilizes a magnetometer, such as a Hall Effect sensor, to sense the heater current using the magnetic field created by the current flow through a wire. However, the Hall Effect sensor is sensitive to ambient magnetic fields, such as those created by the Earth, other components on the aerospace vehicle, and equipment used in testing. Typically, high permeability metal is used to encase and shield the magnetometer from the ambient magnetic field to prevent the ambient magnetic field from influencing the magnetometer's measurement of the heater current. Problems arise with the use of a high permeability metal because the metal is heavy and needed to be fastened to a printed wire board (into which the magnetometer is incorporated) via screws and nuts that are inefficient. Because the shielding effect of the metal is directly proportional to the thickness of the metal, the metal needs to be quite thick to shield the magnetometer from the magnetic field that occurs during vibration testing of the system. Increased thickness results in increased weight and a reduction in efficiency. Therefore, there is a need to develop a current measurement system that does not utilize a high permeability metal to shield the magnetometer.